Synthesis of platinum/multi-wall carbon nanotube catalysts
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The purpose of this research is to investigate the feasibility of the synthesis of platinum/multi-wall carbon nanotube (Pt/MWNT) catalysts and such catalysts’ application in fuel cells. The as-received MWNTs were purified and decorated by pretreatment. Infrared-spectrum indicates the carboxylic (-COOH) and carbonyl (-C⳱O) groups were introduced on the surface of the MWNTs after pretreatment. These functional groups will act as anchor sites for the Pt deposition. Then the Pt particles in nano scale were deposited on the surface of MWNTs by reduction of a solution of hexachloroplatinic acid. Transmission electron microscopy examination reveals that Pt particles are attached to the surface of MWNTs. If as-received MWNTs are not pretreated in the proper way, the Pt particle aggregates are mostly found on the open end of MWNTs. Occasionally Pt penetrated inside the tube of MWNTs. The relationship between the Pt particle morphology and the conditions of pretreatment and reduction reaction is discussed. After heat treatment, Pt particles recrystallized to form the Pt/MWNT catalysts. The Pt/MWNT catalysts were applied to a single cell and the test result shows a promising future of these catalysts with low Pt loading when applied in proton exchange membrane fuel cells (PEMFCs).
I. INTRODUCTION
Fuel cells are receiving increased recognition as notable alternatives to our power sources because they exhibit high operational efficiencies and impressive environmental acceptability. Proton exchange membrane fuel cells (PEMFCs) have great potential for use both in stationary power generation and also as vehicle power sources.1–2 One challenge facing PEMFCs, however, is to improve the use of platinum within the catalyst layer, which should ultimately allow a reduction in the platinum loading at a given fuel cell performance.3–4 Ideally, all of the platinum contained within a PEMFC catalyst layer would be active for the hydrogen-oxidation and oxygen-reduction reactions. The conventional catalyst used for PEMFCs is platinum, supported on carbon (Pt/C).5 The support is usually porous carbon black that has a very large surface area. It is well known that the performance of supported catalysts (namely, the activity, selectivity, and lifetime) depends strongly on the choice of support.6 The most common method for fabricating
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2004.0301 J. Mater. Res., Vol. 19, No. 8, Aug 2004
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the PEMFCs catalyst layer is to mix the Pt/C agglomerates with solubilized polymer electrolyte (such as Nafion ionomer) and apply this paste to a carbon paper. However, because platinum particles deposited within the pores of carbon black may be inaccessible to the polymer electrolyte (Fig. 1), which is necessary to the three-phase reaction zone, it is said that up to 90% of the platinum catalyst in the average easily produced PEMFCs may be inactive.7 Therefore new supports for the Pt catalyst are necessary to impro
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